Alimentary Tube

Colon and Rectum

The colon extends from the cecum to the rectum and consists of ascending, transverse, descending, and sigmoid segments. The cecum is a blind ending pouch extending caudal to the ileocecal valve, typically in the right lower quadrant. The cecum is variably covered in peritoneum and potentially mobile. The appendiceal lumen communicates with that of the cecum. The appendix is notoriously variable in length (up to 20 cm) and location, and can extend far cephalad into the right upper quadrant or caudally into the inguinal canal. It can cross the midline or curl behind the cecum (retrocecal appendix). The ileocecal valve consists of mucosal membrane and circular muscle fibers. It variably allows passage of contrast material on retrograde fluoroscopic studies and is often quite fatty on CT and MRI studies.

The ascending and descending colon and rectum are extraperitoneal, whereas the transverse and sigmoid colon are intraperitoneal, invested in, and suspended by the transverse and sigmoid mesocolons, respectively. The longitudinal muscle of the colon wall is arranged in three parallel bands (taeniae coli), and the contour of the colon is marked by haustrations. Fatty appendages (appendices epiploicae) attach to the serosal surface of the colon. These are normally inconspicuous unless outlined by ascites (Fig. 16-2). On double-contrast barium examination of the colon, one can sometimes see the fine innominate lines (underdistended colon), transverse folds (contracted colon), and lymph follicles that may have central umbilication (young patients) (Fig. 16-3). Lymph follicles can be associated with lymphoma, carcinoma, and inflammatory processes, and when conspicuous in older patients, should prompt a search for an associated abnormality.

Figure 16-2 Contrast-enhanced axial computed tomographic image through the pelvis of a patient with copious ascites demonstrating the normal epiploic appendages.

Figure 16-3 Appearance of lymph follicgles on double-contrast barium enema.

Bowel Wall

The basic layers of the GI tract wall are illustrated in Figure 16-4. The mucosa is best depicted with double-contrast barium studies, although one can only infer information about the bowel wall with fluoroscopy. Using ultrasound (US) under ideal conditions, one can distinctly identify as many as five bowel wall layers (Fig. 16-5). In many circumstances, however, only a central echogenic area (mucosa and submucosa) surrounded by a hypoechoic rim (muscularis propria) can be distinguished.

Figure 16-4 Schematic demonstrating layers of the bowel wall.

Figure 16-5 Ultrasound appearance of bowel wall under optimal conditions.

CT and MRI are usually incapable of resolving the bowel wall to the same extent as US. With contrastenhanced CT, the bowel wall displays stratification during the arterial phase with enhancing mucosa, hypoenhancing submucosa, and moderately enhancing muscularis propria all visible. Visualization of bowel wall layers depends on rate of injection and phase of imaging, and is better appreciated with intraluminal water rather than opaque oral contrast media. The presence of submucosal edema or hemorrhage contributes to a stratified appearance of the bowel.

The normal gastric wall is approximately 5 mm thick as measured between rugal folds in a distended state. The valvulae conniventes of the small bowel are normally less than 2 to 3 mm thick in distended loops, and the normal small bowel wall is only 1 to 2 mm thick when the lumen is sufficiently distended (diameter ≥ 2 cm). The normal colon wall thickness also measures only a few millimeters when adequately distended. Once considered an indicator of inflammatory bowel disease (Fig. 16-6), intramural fat can occur normally in the small intestine and colon of obese patients. This fatty layer becomes less conspicuous with luminal distention.

Figure 16-6 Axial image of the pelvis from a contrast-enhanced computed tomographic scan demonstrates submucosal fat in the distal ileum of a patient with Crohn’s disease.

With any imaging modality, the normal bowel wall can appear thickened if the bowel lumen is not sufficiently distended. It is important to evaluate segments that are distended with gas, fluid, or enteric contrast material to decide whether apparent bowel wall thickening is real, keeping in mind that lumen narrowing can result from mural thickening. Coexisting findings such as adjacent edema, abnormal wall enhancement, or vascular engorgement on CT or MRI examinations can improve diagnostic confidence. Spurious wall thickening tends to be transient, and real-time imaging modalities such as fluoroscopy and US can determine whether an area of questionable wall thickening persists. With many CT and MRI protocols, multiphase or delayed acquisitions are performed, and comparing different phases can help confirm whether an area of bowel wall thickening is fixed or transient. Newer MRI protocols designed to assess the bowel often include rapid imaging sequences such as steady-state free precession that also allow the peristaltic activity of the bowel to be observed.

Bowel Rotation

Normal orientation of the intestinal tract occurs only after the embryologic gut completes a complex series of maneuvers. Failure of any one of these steps results in a variety of congenital abnormalities of the bowel. These developmental maneuvers include elongation of the gut and suspending mesentery, herniation of the gut into the base of the umbilical cord, rotation, and return of the developing gut to the abdominal cavity. It is important to recognize when the process of gut rotation and fixation has gone awry. Box 16-1 lists imaging findings that suggest a gut rotational abnormality. The clinical significance of abnormal rotation and fixation of the bowel is the increased risk for intestinal volvulus, especially in neonates and infants.

Figure 16-7 Nonrotation of the bowel on computed tomography (CT). A, Axial image of the midabdomen from a contrast-enhanced CT scan demonstrates a reversal of the normal relationship of the superior mesenteric artery (SMA) and superior mesenteric vein. B, Coronal reconstruction from the same examination demonstrates abnormal distribution of the large and small bowel.

Radiography (Plain Films)

Radiographs are still widely performed for the evaluation of abdominal complaints. Supine portable radiographs can confirm enteric tube placement, identify calcifications and foreign bodies, suggest a mass or organomegaly, and evaluate for obstruction. The combination of supine and upright radiographs is generally preferred to supine images alone for detection of extraluminal (i.e., intraperitoneal, intramural, or intravascular) gas and for assessment of the bowel gas pattern. Wall thickening can be inferred on abdominal radiography, although the bowel wall is not directly visible in the absence of peritoneal gas (Fig. 16-8). Bowel obstruction causes dilated gas-filled bowel loops proximal to the obstruction, with a lack of gas or bowel contents distal to the obstruction. Dilated fluid-filled bowel loops can escape radiographic detection, although obstruction can be suspected when bubbles of gas collect between mucosal folds (“string-of-pearls sign”).

Figure 16-8 Supine abdominal radiograph of a patient with ulcerative colitis demonstrating thumbprinting of the colon.

Pneumatosis intestinalis can be a subtle finding on radiographs, imparting a bubbly appearance to the bowel that is often mistaken for stool (Fig. 16-9). The presence of pneumatosis should prompt a search for portal venous gas, best seen overlying the periphery of the liver, often on the left of a supine patient. Often, radiographs will be inconclusive in the setting of abdominal pain, and further imaging evaluation will be necessary. Because abdomen radiographs can be the first imaging study for a patient with abdominal pain, timely and accurate interpretation can be critical to patient management and outcome.

Figure 16-9 Supine anteroposterior radiograph of the abdomen demonstrates appearance of pneumatosis involving the right colon.

Fluoroscopy

Fluoroscopic Findings

Box 16-3 and Table 16-1 list key findings visible with GI fluoroscopy. Of course, one must also remember to inspect regions and findings beyond the confines of the GI tract, such as abnormal gas collections, calcifications and other abnormal opacities, organ outlines, and skeletal abnormalities.

BOX 16-3 What to Look for during Fluoroscopy of the Gastrointestinal Tract

Abnormal bowel motility

Abnormal loop configuration or angulation

Separation or displacement of bowel loops

Malposition of bowel

Dilution or flocculation of contrast material

Ulceration

Narrowing

Dilatation

Loss of distensibility

Fold thickening

Fold irregularity or distortion

Diverticula

Filling defects

Extraluminal contrast material

Table 16-1 Fluoroscopic Findings and Their Significance

Finding	Possible Significance
Thickened folds (single or double contrast)	Inflammation, infection, neoplastic infiltration, intramural hemorrhage, or submucosal edema
Radiating folds (single or double contrast)	Normal gastric cardia or pylorus, gastric or duodenal ulcer or ulcer scar
Linear density (double contrast)	Linear ulcer, edge of a protruding lesion, edge of an extrinsic lesion, extrinsic structure viewed through bowel, or coaptation artifact
Ring shadow (double contrast)	Gas-filled diverticulum, polyp surrounded by gas, gas-filled ulcer, gas bubble, or extrinsic structure viewed through bowel (e.g., pedicle)
Double ring shadow (double contrast) (Fig. 16-11)	Polyp on a stalk viewed end-on creates a double ring appearance; this has been referred to as the “Mexican hat sign”; do not confuse this with a barium droplet hanging from sessile polyp or barium pooled in an ulcer crater or diverticulum; in these latter cases, the center of the inner ring will be uniformly dense rather than lucent
Bowler hat (double contrast) (Fig. 16-12)	Sessile polyp (dome of hat points to lumen) or diverticulum (dome of hat points away from lumen)
Focal round density (double contrast)	Stalactite phenomenon (barium dripping from a protruding lesion of the nondependent surface), ulcer, diverticulum, barium precipitate, barium trapped in mucosal fold or pit, or extrinsic density (e.g., calcification)
Filling defect (single contrast) (Fig. 16-13)	Mucosal or submucosal mass, food, stool, foreign body, bubble, blood clot, redundant or nodular mucosa
Bull’s-eye/target lesion (single or double contrast)	Hematogenous metastasis, ulcerated submucosal tumor, aphthous lesion, or ectopic pancreatic rest

Figure 16-11 Image from a double-contrast barium enema demonstrates a pedunculated polyp creating a “double ring shadow.”

Figure 16-12 Image from a double-contrast barium enema demonstrates a sessile polyp of the transverse colon.

Figure 16-13 Spot film from a single-contrast barium examination of the stomach demonstrating a small hyperplastic antral polyp.

Ultrasound

In the United States, ultrasound is rarely used as a stand-alone technique for assessment of bowel. In most general radiology practices, it is more likely that a bowel abnormality will be discovered incidentally during an abdominal sonographic survey than as the result of a directed search (Fig. 16-14). It is perhaps most important that one be able to distinguish between normal and abnormal bowel with US, because additional diagnostic tests will likely be necessary before a definitive diagnosis can be established.

Figure 16-14 Abnormal-appearing colon discovered incidentally in a patient with pseudomembranous colitis undergoing ultrasound of the kidneys and bladder.

Normal bowel is compressible by the US transducer, and peristalsis can be observed during real-time imaging. Water administered by mouth or per rectum aids in distinguishing bowel from other structures or conditions such as abscess. Normal bowel typically demonstrates some degree of stratification with US, and interruption of any of the bowel wall layers may be a sign of abnormality such as tumor. A thick hypoechoic ring (representing thickened bowel wall) surrounding a hyperechoic residual lumen, ulcerated mucosa, or both is referred to as the “pseudokidney sign.” This appearance is reasonably predictive of bowel pathology.

When bowel wall thickening is present, one should attempt to distinguish between short-segment thickening (more worrisome for a malignant process) and longsegment thickening (more likely with benign processes such as inflammation or infection). Bowel wall tumors are usually hypoechoic. Increased echogenicity in the fat adjacent to bowel may be a sign of inflammation. Gas trapped in ulcerated mucosa produces linear echogenic foci often associated with ring-down artifact. Pneumatosis produces echogenic foci in the bowel wall that can shadow. The normal bowel wall shows minimal signal with color Doppler. Completely absent flow with color Doppler can be a sign of intestinal ischemia, whereas increased flow suggests inflammation or neoplasia.

Pelvic bowel loops that are difficult to evaluate transabdominally may be better visualized with transvaginal US, although transvaginal US is rarely performed for this indication. Endorectal US is commonly performed for the staging of rectal carcinoma. Although endorectal US cannot assess distant disease, it is a relatively accurate method of determining T stage of rectal cancer. Loss or discontinuity of the normal layered appearance of the rectal wall implies tumor invasion. Endoscopic US is also useful for the diagnosis and staging of gastric tumors, and it has the advantage of facilitating biopsy of any abnormalities encountered.

Computed Tomography

With appropriate patient preparation, protocol design, and reconstruction techniques, CT is an excellent means of assessing the GI tract (Box 16-4). CT excels at the detection of inflammatory and neoplastic processes that affect the bowel, even when patient preparation and cooperation are less than optimal. CT has replaced other methods of detecting the presence, site, and cause of bowel obstruction. CT enterography (without small-bowel intubation) and enteroclysis (with small-bowel intubation) are used increasingly to evaluate small-bowel disorders, and CT colonography may soon become the preferred method of screening patients for colon polyps and cancer (Fig. 16-15). Currently, most nonpolypoid mucosal processes, small vascular malformations, motility disorders, and malabsorptive states cannot be reliably and routinely diagnosed with CT.

Figure 16-15 Endoluminal view from a computed tomography colonographic study. The colon lumen is distended with gas administered per rectum after a bowel prep.

Magnetic Resonance Imaging

Nuclear Medicine

Nuclear scintigraphy has a limited but important role in evaluating the GI tract. Table 16-2 lists potential applications to consider.

Table 16-2 Potential Indications for Nuclear Scintigraphy of the Gastrointestinal Tract

Positron emission tomography (PET) utilizing F-18 fluorodeoxyglucose (¹⁸F-FDG) is revolutionizing oncologic imaging. Because cancer cells often demonstrate higher metabolic activity than normal cells, the uptake of glucose by many cancer cell types is generally greater. ¹⁸F-FDG is a glucose analog that is handled in much the same way by cells as glucose. Within the GI tract, PET imaging with ¹⁸F-FDG is used primarily to stage and assess response to therapy for esophageal and colorectal carcinoma. PET may also detect malignant tumors from non-GI sites that secondarily involve the bowel.

Capsule Endoscopy

Capsule endoscopy has supplanted small-bowel fluoroscopic studies in searching for mucosal lesions, particularly in patients with occult GI bleeding. It should not be used, however, if there is suspicion of bowel stricture or obstruction.

Thickening

Deciding whether the gastric wall is too thick on an imaging study is a challenge, because the gastric wall varies in thickness between its nondistended and distended states. If the study is performed specifically to evaluate the stomach, every reasonable effort should be made to completely distend the lumen by using effervescent granules, water, or other oral contrast material. When only partial distention of the stomach can be achieved, changing the patient’s position can redistribute the gastric contents to distend individual gastric segments. The gastric wall between rugal folds generally measures 5 mm or less. The gastric cardia looks thickened and masslike when not adequately distended, mimicking a carcinoma on CT. The distal antrum and pyloric channel are also common locations of spurious thickening on CT and MRI. Giving gas crystals and scanning the patient left-side-down can help to differentiate real from artifactual thickening. As a general rule, the prepyloric antral wall of the stomach should measure less than 5 mm. The antrum should be considered abnormal when this thickness exceeds 10 mm or if asymmetric thickness is present.

Normally the gastric wall is thinner in nondependent segments of the stomach that are well distended by gas. In addition, adherent debris that may add to the appearance of gastric wall thickening typically remains within the fluid-filled dependent portions. When wall thickening involves not only dependent, fluid-filled parts of the stomach but also nondependent, gas-filled portions on a CT or MRI scan, an underlying abnormality should be suspected (Fig. 16-18).

Figure 16-18 Enhanced axial computed tomographic scan through the abdomen of a patient with B-cell lymphoma involving the stomach.

Thickening of the rugal folds has an extensive differential diagnosis (Table 16-3). Fortunately, many of the entities that cause rugal fold thickening are extremely rare, and many of the common causes will have other imaging findings that allow a specific diagnosis to be made.

Table 16-3 Causes of Rugal Fold Thickening

Figure 16-19 Spot film from a single-contrast barium examination of a patient with rugal fold thickening caused by gastric lymphoma.

Figure 16-20 Axial image from a contrast-enhanced computed tomographic scan through the upper abdomen of a patient with lymphoma involving the stomach.

Gastric adenocarcinoma can cause focal or diffuse gastric wall thickening, although the normal rugal fold pattern is typically not maintained at the site of tumor. Scirrhous carcinoma infiltrates the submucosa of the stomach, resulting in some combination of wall thickening, luminal narrowing, and reduced distensibility. Gastric lymphoma can have a variety of appearances including diffuse gastric wall thickening (see Fig. 16-18).

Luminal Narrowing

Gastric narrowing is often more apparent on barium examination of the stomach than on cross-sectional imaging studies, because most causes of gastric narrowing also result in reduced distensibility and hypomotility. The antrum is the most commonly narrowed gastric segment, and wall thickening often accompanies luminal narrowing. Clinical history plays an important role in distinguishing causes of gastric narrowing (e.g., history of caustic ingestion, radiation treatment, known primary neoplasm). Table 16-4 lists some causes of gastric narrowing.

Table 16-4 Causes of Gastric Narrowing

Dilatation

Gastric dilatation is often associated with a history of nausea, vomiting, or both, although asymptomatic gastric distention is not uncommon. The causes of gastric dilatation can be divided into two major groups: (1) functional obstruction or atony from a wide variety of causes, such as prior vagotomy, medications, diabetes, uremia, ischemia, trauma, or scleroderma; and (2) mechanical outlet obstruction from abnormalities such as tumor, ulcer, inflammatory stricture, pancreatitis, bezoar, prolapsed polyp, or volvulus. A distended, gas-filled stomach can be seen in patients after resuscitation or instrumentation. When a dilated stomach is encountered on an imaging examination, one must always closely examine the gastric outlet, duodenum, and surrounding structures for possible causes.

Ulceration

With the widespread availability of endoscopy and development of effective methods of treating peptic ulcer disease, gastric ulcers are rarely encountered by radiologists. Many radiologists will have never diagnosed a gastric ulcer on an upper GI examination during their training.

Most gastric ulcers are found along the posterior wall of the antrum or body, or along the lesser curvature of the stomach. Anterior wall or greater curvature ulcers account for about 15% of gastric ulcers. Of course, this statistic is not particularly useful to the radiologist faced with one particular ulcer on a fluoroscopic study. It is far more useful to know whether to recommend endoscopy for further evaluation when encountering a gastric ulcer. In general, endoscopy should be pursued if any ulcer is less than unequivocally benign in appearance (Table 16-5). Although the other signs are useful from a statistical standpoint, only the rarely seen Hampton line is believed to be an unequivocal sign of benignity.

Table 16-5 Features Suggestive of Benign versus Malignant Gastric Ulcers

* Hampton line refers to a thin, straight lucent line across the neck of a contrastfilled ulcer representing intact mucosa.

† Carman meniscus sign is created when the heaped-up edges of a large shallow malignant ulcer are apposed during compression, trapping barium in a collection that is convex to the gastric lumen.

Erosions are small, superficial linear or round ulcerations that often occur on the crests of gastric folds. Erosions are typically multiple and often demonstrate a radiolucent halo of edematous mucosa on double-contrast barium examinations. Box 16-6 lists some causes of gastric erosions. Note that many of the entities that cause erosions also can result in gastric wall thickening and narrowing when advanced.

Masses

Pseudotumors

The stomach is a common site for a false-positive interpretation regarding a mass. Some common locations for gastric pseudotumors include the region of the gastric cardia, along the proximal lesser curvature, and in the distal antrum and pyloric region. Most often, the appearance of a mass is related to redundant, contracted, or nondistended gastric wall, and the issue can be satisfactorily resolved with further distention of the stomach. Ingested material or bezoar may also give the false impression of a gastric mass (Fig. 16-21). A pseudotumor can change dramatically in position, often does not have a consistent connection with the gastric wall, and may fail to demonstrate enhancement after intravenous contrast administration on CT and MR images. A true gastric neoplasm is a persistent finding on multiple phases, acquisitions, or examinations that has a consistent communication with the gastric wall and demonstrates enhancement. Movement alone is not a helpful sign because pedunculated gastric masses can change position. Unlike some bezoars, gastric neoplasms do not contain gas. A pancreatic rest can simulate an ulcerated submucosal mass. Ectopic pancreatic tissue usually occurs along the greater curvature of the distal gastric antrum or in the proximal duodenum. Pancreatic rests are usually small (1 cm or less), broad based, smooth, and have a central umbilication related to the primitive ductal system as seen on barium studies.

Figure 16-21 Axial image from a contrast-enhanced computed tomographic scan through the stomach of a patient with a large bezoar.

Pitfall: Pseudotumors of the stomach commonly occur in the region of the gastric cardia, along the proximal lesser curvature, and in the distal antrum and pyloric region.

Gastric Polyps

Gastric polyps are common mucosal masses of the stomach. Gastric polyps can be adenomatous, hyperplastic, or hamartomatous (Fig. 16-22). Most gastric polyps are hyperplastic, whereas in the duodenum, most polyps are adenomatous. Hyperplastic polyps are often small (<1 cm), smooth, sessile, and multiple. Adenomatous polyps are frequently solitary and more likely to be large (>2 cm) and pedunculated (Table 16-6).

Figure 16-22 Spot film from a single-contrast upper gastrointestinal examination demonstrates an antral polyp.

Table 16-6 Adenomatous versus Hyperplastic Gastric Polyps

Feature	Adenomatous	Hyperplastic
Size	>1 cm	<1 cm
Shape	Lobulated	Smooth
Number	Solitary	Multiple
Base	Sessile or pedunculated	Sessile

Pearl: Most gastric polyps are hyperplastic, whereas most duodenal polyps are adenomatous.

Submucosal Mass

Submucosal masses typically have borders that are mildly obtuse with respect to the gastric wall, although some submucosal masses will appear pedunculated, potentially creating confusion with gastric polyps. Most benign submucosal masses are smooth with intact overlying gastric mucosa, although central ulceration or umbilication can occasionally create a bull’s-eye appearance. Definitively characterizing a submucosal mass with imaging is difficult in most cases. Occasionally, some clues as to causative factors exist. Lipomas and lymphangiomas are compressible and can be seen to change shape. Lipomas are fat density, whereas lymphangiomas are cystic on CT images. A lesion that contains phleboliths represents a hemangioma. A solitary, smooth, round, submucosal soft-tissue mass or a large, exophytic, necrotic mass are statistically most likely to represent leiomyoma or gastrointestinal stromal tumor (GIST) (Fig. 16-23). Box 16-7 lists some causes of submucosal mass.

Figure 16-23 Axial image of the abdomen from computed tomography performed with positive oral contrast material but no intravenous contrast in a patient with a gastrointestinal stromal tumor of the stomach.

BOX 16-7 Submucosal Gastric Masses

Leiomyoma (leiomyosarcoma)

GIST

Lymphoma

Lipoma

Hemangioma

Neurogenic tumors (e.g., neurofibroma)

Metastasis

Varix

Common Malignant Gastric Tumors

GASTROINTESTINAL STROMAL TUMOR

GISTs are histologically distinct from leiomyomas, although this distinction cannot be made with imaging. Likewise, the distinction between benign or malignant is difficult unless metastatic disease or frank invasion is present. Most GISTs are sporadic, but these tumors can be associated with neurofibromatosis (NF-1) and Carney triad (gastric GIST, pulmonary chondroma, extraadrenal paraganglioma). GISTs are usually solitary, often large, round tumors of the gastric wall. They can appear primarily exophytic (common), intramural, or endophytic (i.e., bulging into gastric lumen [least common]). GISTs are often necrotic, demonstrating mucosal ulceration or deep cavitation that can communicate with the gastric lumen. Up to 25% of lesions demonstrate calcifications on CT. GISTs usually are of intermediate signal intensity on T1-weighted MRI and intermediate to low signal intensity on T2-weighted MRI. Areas of central necrosis demonstrate increased signal intensity on T2-weighted images. Enhancement after intravenous contrast administration is variable on CT and MRI (necrotic areas do not enhance). GISTs tend to be ¹⁸F-FDG avid. Therefore, PET is a useful modality for documenting early response to imatinib. Malignant tumors can spread to liver, peritoneum, and rarely, lymph nodes. Metastatic foci often resemble the primary tumor, although metastases treated with imatinib can mimic cysts.

Pearl: GISTs are often necrotic, demonstrating mucosal ulceration or deep cavitation that can communicate with the gastric lumen.

Pitfall: Metastases treated with imatinib can mimic cysts.

ADENOCARCINOMA

Most gastric cancers are adenocarcinomas. Adenocarcinomas can be polypoid, plaquelike, endophytic, exophytic, or infiltrative. Unlike stromal tumors, most adenocarcinomas present as endophytic masses or irregular focal wall thickening (Fig. 16-24). Ulceration is relatively common. Scirrhous carcinoma results in a thickened nondistensible stomach (linitis plastica appearance). Gastric cancer can be associated with malignant ascites, peritoneal nodules, or regional lymphadenopathy.

Figure 16-24 Axial image from a computed tomographic scan performed through the upper abdomen with positive oral contrast material in a patient with gastric adenocarcinoma.

LYMPHOMA

Lymphoma often presents with thicker and more diffuse circumferential involvement of the stomach than other tumors (see Fig. 16-18). Despite this, the stomach involved with lymphoma often remains distensible. As elsewhere in the body, lymphoma is a great mimicker of other diseases. When presenting as a large, solitary, ulcerated mass, lymphoma can be indistinguishable from a GIST. Hodgkin’s lymphoma can be scirrhous or present as thickened rugal folds. MALT lymphoma is a low-grade B-cell lymphoma associated with Helicobacter pylori infection. MALT lymphoma can present as multiple round, confluent nodules. Lymphadenopathy in a distribution other than the gastric drainage is a clue that a gastric mass represents lymphoma, although lymphadenopathy is not a conspicuous feature of MALT lymphoma. Gastric outlet obstruction is uncommon with lymphoma.

Pearl: The stomach involved with lymphoma can remain distensible and rarely becomes obstructed.

SECONDARY TUMORS

Malignant tumors can spread to the stomach via hematogenous spread, direct spread from contiguous organs, and peritoneal spread (Fig. 16-25). Breast cancer, lung cancer, and melanoma are among the more common malignant neoplasms to metastasize to the stomach. Hematogenous metastases can mimic primary gastric tumors such as adenocarcinoma or GIST, although the classic appearance is one of multiple centrally ulcerated submucosal masses (bull’s-eye lesions). Breast cancer involving the stomach can cause a linitis plastica appearance. Pancreatic cancer and colon cancer can spread to the stomach directly, whereas other tumors can involve the stomach via the gastric mesenteries. Direct invasion of the stomach from a nongastric primary results in spiculation and/or tethering of the involved wall with distortion of the mucosal folds. CT reveals a soft-tissue mass obliterating the fat planes between the stomach and the organ of origin.

Figure 16-25 Axial image of the upper abdomen from contrast-enhanced computed tomographic scan of a patient with melanoma metastatic to the stomach.

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